She hurried home and dyed her hair, then came back and again told the salesman, "I would like to buy this TV." 

"Sorry, we don't sell to blondes," he replied.

"Darn, he recognized me," she thought. She went for a complete disguise this time, haircut and new color, new outfit, big sunglasses, then waited a few days before she again approached the salesman. "I would like to buy this TV." 

"Sorry, we don't sell to blondes," he replied.

Frustrated, she exclaimed, "How do you know I'm a blonde?" 

"Because that's a microwave." he replied.